Prosthetic heart valves have been in use for approximately fifteen years, but relatively little is known about prosthetic heart valve effects on blood flow. Even less is known about the long term effects associated with heart valve replacement on blood cell elements and arterial walls. The proposed research is a collaborative study between cardiologists, engineering scientists and cardiac surgeons to measure the fluid dynamic effects of aortic valve replacement on coronary blood flow and aortic blood flow. Dynamic left ventricle-aortic model studies of prosthetic heart valve systems under both steady flow and pulsatile conditions will be related to animal and patient measurements. Both the in vivo and in vitro phases of the work will make use of hot film anemometer techniques. Specifically, velocity profiles, turbulence intensities and shear stresses will be measured in: 1) a model aorta before and after aortic valve replacement under steady flow conditions, 2) a model aorta before and after aortic valve replacement under pulsatile conditions, 3) normal dogs before and after aortic valve replacement and 4) patients with aortic valve disease before and after aortic valve replacement at the time of open-heart surgery. In the dog studies, electromagnetic coronary flow and regional coronary flow (microspheres) will also be measured. These studies should result in a better understanding of flow turbulence and shear downstream of the aortic valve. In a fundamental sense, this will advance our understanding of: 1) the physiologic significance of pulsatile flow on blood vessel walls and blood elements; 2) the engineering constraints on mechanical heart prosthesis systems and 3) basic flow velocity parameters necessary to develop more sophisticated mathematical models of blood flow. In a more practical sense, it will allow a better understanding of aortic valve replacement on: 1) distribution of coronary blood flow; 2) mechanism of ascending aortic atherosclerosis and 3) increased work of the heart due to aortic valve replacement.